Design of Adaptive Super Twisting Sliding Mode Control with PID-Based Sliding Surface for Rudderless Flying-Wing UAVs

The rudderless flying-wings are fixed-wing type UAVs without horizontal and vertical stabilizers. The robust control problem of this category of UAVs is of great importance due to strong coupling between reduced control surfaces and longitudinal/lateral mode, misbehaving dynamics, non-minimum phase nature of lateral mode, high sensitivity to control surface commands, disturbances, and uncertainties. The second-order super twisting sliding mode method is one of the uncertainty-resistant control algorithms, which is especially implemented in non-linear models. By combining this controller with adaptive methods, the control gains are not overestimated despite the uncertain disturbance bounds. Furthermore, by adding an integral term to the standard sliding surface equation based on the tracking error, the sliding surface is defined in PID form, which helps to increase the tracking accuracy. The comparison of the proposed method with the non-adaptive and simple adaptive super twisting sliding mode control methods demonstrates the proper performance of the proposed method in longitudinal tracking control behavior in the presence of uncertainties and disturbances.